Below is a single, opinionated, **Debian-only** decade scheme that you can clone into `/etc/linux-decades/` (or keep in Git and symlink).  
Everything is pure Debian tooling—`apt`, `debconf`, `systemd`, `sysctl.d`, `sudoers.d`, `nftables`, etc.—no network-centric artifacts.

Directory layout (drop-in ready):

```
/etc/linux-decades/
├── 00_bootstrap/
│   ├── 00_00_installer_seed.cfg          # preseed / cloud-init
│   ├── 00_10_register_debian_mirror.sh   # sources.list generator
│   └── 00_20_first_boot_update.sh
├── 10_system/
│   ├── 10_00_hostname_timezone.sh
│   ├── 10_10_ntp_chrony.conf
│   ├── 10_20_dns_resolved.conf
│   └── 10_30_sysctl_hardening.conf
├── 20_identity/
│   ├── 20_00_users_groups.yml          # Ansible / plain YAML for loop
│   ├── 20_10_sudoers.d/                # one file per rule
│   ├── 20_20_sshd_config_fragment.conf
│   └── 20_30_authorized_keys/          # keys by username
├── 30_storage/
│   ├── 30_00_luks_btrfs_subvols.sh
│   ├── 30_10_lvm_thinpool.sh
│   ├── 30_20_fstab_mounts.conf
│   └── 30_30_zram_generator.conf
├── 40_packages/
│   ├── 40_00_sources_list_debian.sh
│   ├── 40_10_essential_packages.lst
│   ├── 40_20_backports_pin.pref
│   └── 40_30_flatpak_remote.sh
├── 50_services/
│   ├── 50_00_unit_templates/
│   │   ├── backup@.service
│   │   └── podman@.service
│   └── 50_10_enable_units.sh          # systemctl preset-all helper
├── 60_runtime/
│   ├── 60_00_nginx_sites/
│   ├── 60_10_postgres_conf.d/
│   ├── 60_20_logrotate_d/
│   └── 60_30_cron_dropins/
├── 70_performance/
│   ├── 70_00_cgroup_v2_enable.sh
│   ├── 70_10_cpu_governor.sh
│   ├── 70_20_irqbalance_ban.conf
│   └── 70_30_tuned_profile.conf
├── 80_security/
│   ├── 80_00_nftables_rules.nft
│   ├── 80_10_fail2ban_jail.local
│   ├── 80_20_apparmor_profiles/
│   └── 80_30_aide_daily.timer
└── 90_local/
    ├── 90_00_site_overrides.sh
    └── 99_zz_last_minute_fix.sh
```

Minimal glue to wire it together

1. Create `/etc/linux-decades/apply.sh`:
   ```bash
   #!/bin/bash
   set -euo pipefail
   for d in /etc/linux-decades/*/; do
       for f in "$d"*; do
           [[ -x "$f" ]] && "$f"
       done
   done
   ```
   Make it executable.  
   Run once at first boot, or from a systemd one-shot.

2. One-shot systemd unit (`/etc/systemd/system/decades-apply.service`):
   ```
   [Unit]
   Description=Apply decade-scheme configuration
   ConditionPathExists=!/var/lib/decades-applied.stamp

   [Service]
   Type=oneshot
   ExecStart=/etc/linux-decades/apply.sh
   ExecStartPost=/bin/touch /var/lib/decades-applied.stamp
   RemainAfterExit=yes
   ```
   Enable it so first boot only triggers once.

3. Optional `debconf` integration  
   Use `db_get`/`db_set` in decade-00 scripts if you want fully unattended installs.

Golden rules (to keep it “perfect”)

• Filenames **must** start with their decade prefix (`00_`, `10_`, …).  
• Every executable script must be idempotent (safe to run twice).  
• Non-executable snippets (`.conf`, `.d/` drop-ins) are copied or symlinked by a small helper in the same decade directory.  
• Never put anything in `90_local/` that you expect to keep—treat it as a parking lot for today’s emergency patch.

Drop this tree into Git, clone to any new Debian box, run `apply.sh`, and your decade scheme is live.